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ECE :: Materials and Components

  1. The resistivity of intrinsic semiconductors, at room temperature, is of the order of

  2. A.
    1 Ω-m
    B.
    1000 Ω-m
    C.
    106 Ω-m
    D.
    10-3 Ω-m

  3. Assertion (A): Ferromagnetic materials possess ferromagnetic properties only when temperature is less than paramagnetic curie temperature.

    Reason (R): For a ferromagnetic material for T > θf.

  4. A.
    Both A and R are true and R is correct explanation of A
    B.
    Both A and R are true but R is not correct explanation of A
    C.
    A is true but R is false
    D.
    A is false but R is true

  5. In terms of classical representation of electrons

  6. A.
    an atom is essentially empty
    B.
    an atom is essentially full
    C.
    an atom may be essentially empty or full depending on the material
    D.
    an atom may be essentially empty or full depending on temperature

  7. To produce magnetic flux, mmf is necessary.

  8. A.
    True
    B.
    False

  9. For a polyatomic gas, the equation relating dielectric constant ∈r with molecular properties is


  10. The relaxation time of electrons in a metal is of the order of

  11. A.
    10-6 secs
    B.
    10-10 secs
    C.
    10-14 secs
    D.
    10-20 secs

  12. Assertion (A): For elemental dielectrics, P = NaeEi where N is number of atoms/m3, P is polarization, ae is electronic polarization and Ei is internal electric field.

    Reason (R): In elemental dielectrics there are no permanent dipoles or ions.

  13. A.
    Both A and R are true and R is correct explanation of A
    B.
    Both A and R are true but R is not correct explanation of A
    C.
    A is true but R is false
    D.
    A is false but R is true

  14. The circumference of an electron orbit is equal to integer times the wavelength of electron.

  15. A.
    True
    B.
    False

  16. In a specimen of silicon steel, a field strength of 200 A/m causes a flux density of 0.5 T. In a specimen of cast iron, the same H would cause B to be

  17. A.
    0.5 T
    B.
    less than 0.5 T
    C.
    more than 0.5 T
    D.
    0.5 T or more or less

  18. In a rare gas, the molecules of some atoms have an excess positive or negative charge. The electric field tends to shift positive ions relative to negative ions. This is known as ionic polarization.

  19. A.
    True
    B.
    False